The present invention relates to a method for identifying a data area which is reserved in accordance with a first specification but may contain useful data in accordance with a second specification, and corresponding apparatuses and data carriers.
Fields which are reserved fields in accordance with a first version of a standard, hereinafter mostly referred to as first specification, may have to be utilized by apparatuses of later versions of the standard, hereinafter mostly referred to as second specification, for example in order to enable further functions which had not yet been taken into consideration at the time when the first specification was defined. For this purpose, however, there must be a clear definition of how apparatuses of earlier versions handle these fields. Handling includes, inter alia, reading, writing or editing the data of the data carrier.
The reserved fields have hitherto been ignored in accordance with the earlier versions of a specification. Only more recent versions of the specification utilize the reserved fields. This has the disadvantage that the earlier versions of the specification do not prescribe how these fields reserved in accordance with the earlier version are to be handled in the event of editing, that is to say firstly reading, then changing, then rewriting. The reserved fields then have an undefined content and cannot be correctly interpreted by apparatuses which operate in accordance with the more recent version. Consequently, compatibility between apparatuses of different versions of a specification is not ensured.
It is an object of the invention to propose a method which enables compatibility between different versions of a specification, hereinafter referred to as first specification and second specification, and corresponding apparatuses and data carriers.
According to the invention, in order to identify a data area, which is reserved in accordance with a first specification, as containing useful data in accordance with a second specification, it is provided that a header area assigned to the reserved data area is present, which header area, in the event of transmission, is provided with a status information item xe2x80x9creservedxe2x80x9d if the reserved data area contains no or no checked useful data in accordance with the second specification, and, in the event of transmission, is provided with a status information item xe2x80x9cvalidxe2x80x9d if the reserved data area contains useful data in accordance with the second specification. In the event of reception, a status information item is taken from the header area, the reserved data area, in the case of status information xe2x80x9cvalidxe2x80x9d, being identified as containing valid useful data in accordance with the second specification, or else as containing no or no checked useful data in accordance with the second specification if the status information xe2x80x9creservedxe2x80x9d is present. This method has the advantage that reserved data areas can be received and/or transmitted both by apparatus which operate according to the first specification and by those which operate according to the second specification, without compatibility problems arising. In this case, transmission means both line-based or line-free transmission and recording on storage media. The latter are to be regarded as, for example, data carriers such as optical recording media CD or DVD, magnetic recording media, memory modules, in each case both unwriteable and writeable, irrespective of their physical construction. Reception is to be regarded as both the reading of such storage media and the reception of data transmitted in a line-based or line-free manner. The reserved data area generally contains no useful data if it falls completely under the first specification. By contrast, it contains no checked data if data which correspond to the second specification are transmitted in accordance with the first specification.
For an apparatus which operates according to the first specification, the second specification is absent. According to the invention, it does not evaluate as useful data the data contained in the reserved data area, even if these are created in accordance with the second specification, and the status information thus indicates xe2x80x9cvalidxe2x80x9d. These useful data are ignored for the evaluation, that is to say, for example, the conditioning for representation on a screen or another suitable outputting or further processing. This has the advantage that data transmitted in accordance with the second specification do not lead to an undefined behaviour of an older device operating according to the first specification, but rather merely to the absence of certain functions which are not present anyway in accordance with the first specification.
According to the invention, useful data which are created in accordance with the second specification, but are received in accordance with the first specification, are transmitted unchanged. This has the advantage that the corresponding information is not lost even if it is transmitted in an intermediate step in accordance with the first specification.
If the reserved data area is assigned a data block, then, according to the invention, the status information xe2x80x9cvalidxe2x80x9d is used for transmission purposes if the data block is transmitted unchanged. By contrast, if the data block is transmitted in changed form, then the status information is set to xe2x80x9creservedxe2x80x9d. This has the advantage that, in the event of totally unchanged transmission of the received data, the content thereof is not changed even if reception and transmission are effected in accordance with the first specification. In this case, it can be assumed that the useful data in the area reserved in accordance with the first specification are correct. By contrast, if a change to the data contained in the data block has been performed after reception, then this can result in the correctness of the useful data contained in the area reserved in accordance with the first specification, for example if the said useful data are combined with data situated in the associated data block. In this case, the status information is set to xe2x80x9creservedxe2x80x9d and an apparatus operating in accordance with the second specification recognizes that the corresponding useful data should at least not be used unchecked. The data block assigned to the reserved data area can perfectly well be fragmented, in other words need not comprise a contiguous piece; it can either include the reserved data area or be separate from the latter. However, the way in which the data block assigned to the reserved data area is defined must already be fixed in the first specification.
According to the invention, not only a change in the content of a data block but also a change in the latter""s relative position, for example in the temporal sequence of a plurality of data blocks or the spatial arrangement relative to other data blocks, is regarded as a change in the data block. This has the advantage that even combinations of the useful data which are connected with this relative position and are impaired by the new arrangement are not regarded as checked.
In accordance with the invention, it is furthermore provided that in the absence of the second specification, a newly created or copied reserved data area is transmitted with status information xe2x80x9creservedxe2x80x9d and useful data of the value zero. This has the advantage that apparatuses of the second specification can distinguish the copied data areas from the original data area. That is expedient since an apparatus of the first specification cannot know whether the useful data generated by means of the second specification are still valid as copy. In case of doubt, it is therefore expedient to initialize the reserved area of the copied data area according to the rules of the first specification.
According to the invention, given the presence of the second specification and reception of a reserved data area identified with status information xe2x80x9creservedxe2x80x9d, the content of the said data area is checked for validity using the second specification and, if this validity exists, is regarded as valid useful data in accordance with the second specification for evaluation and/or transmission purposes. This has the advantage that useful data whose conceptual content may have been changed are also checked and, if the conceptual content is unchanged, are regarded as correct for further processing and are also marked as such in the event of transmission. Such checking using the second specification consists, in a simple case, in checking whether or not the corresponding data have a combination with data of the data block. In the latter case, they are regarded as correct. In another case, the checking consists for example in a plausibility check which is carried out using the boundary conditions prescribed in the second specification.
It is advantageous that in the specification, both in the first and in the second specification, it is additionally stipulated that there is also stored or transmitted the version number of the specification according to which the apparatus which was the last to change or augment the data operates. Consequently, apparatuses of a certain specification, when receiving the data, can immediately assess which data can still be valid for them, and which cannot. The storage of the version number is performed for example using two bytes. In this case, the first byte contains the version number element to the left of the point and the second byte contains the version number element to the right of the point. Example: for the version 12.34, 12 is stored in the first byte and 34 is stored in the second byte.
It is advantageous that a further type of reserved data areas is also provided, which can be identified in accordance with a different method. This increases the flexibility of the configuration of the different specifications.
The header area preferably consists of a single bit. This requires only a small consumption of usable data area. In certain cases, it is expedient to provide larger header areas, for example if it is already known that a plurality of different versions will follow the first specification.
If the entire reserved data area for useful data is not required for the second specification, then, according to the invention, the data area reserved in accordance with the first specification is divided, in accordance with the second specification, into a first useful data area and a second, reserved area, which is then provided for receiving useful data in accordance with a further, future specification.
An apparatus according to the invention for receiving and/or transmitting data which may contain data areas reserved in accordance with a first specification identifies these as containing useful data in accordance with a second specification, by one of the methods mentioned above.
A data carrier according to the invention, which data carrier has data areas which are reserved in accordance with a first specification and contain useful data in accordance with a second specification, has a header area for a reserved data area, in which header area the data area is identified as reserved in accordance with a first specification or containing useful data in accordance with a second specification. This data carrier can be identified with regard to the reserved data area preferably in accordance with one of the methods mentioned above.
Further advantages of the invention are specified in the following description of advantageous configurations of the invention. It is understood that supplementations or modifications that are within the abilities of persons skilled in the art likewise lie within the scope of the invention.